Power system including rotary transformers



y 1942- H. s. MOORE ETAL 74 POWER SYSTEM INCLUDING ROTARY TRANSFORMER Filed Feb. 20, 1941 2 Sheets-Sheet-l MOTORING Inventors: Harold G. Moore, Fremont Felix,

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May 12, 1942. O ETAL 2,282,874

POWER SYSTEM INCLUDING ROTARY TRANSFORMER Filed Feb. 20, 1941 2 Sheets-Sheet 2 Pig. 2.

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Their Attorney Patented May 12, 1942 POWER SYSTEM INCLUDING ROTARY TRAVSFOI KMERS Harold G. Moore, Wesleyville, Pa., and Fremont Felix, Schenectady, N. Y., assignors to General Electric Company, a corporation of New York Application February 20, 1941, Serial No. 379,794

20 Claims.

Our invention relates to power systems including direct-current rotary transformers of the armature reaction excitation type, and more particularly to power systems wherein the driving motors are connected between the primary and secondary brushes of the rotary transformers.

Various systems have been devised for providing smooth acceleration of direct-current motors adapted to be connected substantially directly across the source of electrical power supply through a device or devices which inherently regulate the electrical potential and current of the motors during acceleration and normal running and which also utilizes the motors to provide a retarding or braking force. It has been found that these characteristics can readily be obtained in a power system using a rotary transformer of the armature reaction excitation type connected to the source of power supply with a proper arrangement for connecting each of the driving motors across a brush of the transformer primary brushes and a brush of the transformer secondary brushes. This general type of system has been described in detail in U. S. Patent No. 1,969,699, J. M. Pestarini, wherein a m'etadyne rotary transformer is used to supply the power to driving motors connected as described above. Such a system provides twoload loop circuits through the armatui'e of the rotary transformer and includes an external load in each loop and has been termed an 8-connection, 'One of the difiiculties which has been encountered in such a system is to insure against the generation of too high a voltage by the motors during regenerative braking and also to provide for the absorption of power generated by the motors during braking periods when the connection between the transformer primary brushes and the source of power supply may be broken or when a shortcircuit may occur on the source of power supply.

An object of our invention is to provide a power system having an arrangement for utilizing the driving motors to provide a retarding or braking force to a driven vehicle and to insure the absorption of the power generated during these periods.

Another object of our invention is to insure against the application of excessive voltages to the brushes of a rotary transformer by the driving motors during braking operation.

A further object of our invention is to provide a smooth acceleration of the driving motors when connecting this type system to a source of electrical power supply for motoring purposes.

Further objects and advantages of our invention will become apparent and our invention will be better understood from the following description referring to theaccompanying drawing, and the features of novelty which characterize our invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In the drawings, Fig. 1 illustrates a power system wherein an'armature reaction excited rotary transformer is adapted to supply power from a source of power supply to driving motors connected to the transformer in figure 8" connection and including starting and braking resistances with an arrangement forconnecting these resistances to provide the desired operating characteristics to the system; Figs. 2 and 3 show characteristic curves of an-exciter of the system when certain of its field exciting windings are energized; and Figs. 4 and 5 are the resultant operating characteristics thereof.

Referring to the drawings, we have shown a power system particularly adapted for use in driving traction vehicles. Electrical power is adapted to be supplied to the vehicle from a third rail or trolley 10 with one side grounded as at H. An armature reaction excited dynamo-electric machine such as a rotary transformer 12 having an armature and a commutator is provided with primary brushes l3 and I4 adapted to be connected to the source of power supply and secondary brushes l5 and I6 electrically displaced about the commutator from the primary brushes I3 and H. An electrical load comprising a driving motor [1 is adapted to be connected to the primary brush l3 and the secondary brush l5 and another driving motor [8 is adapted to be connected between the secondary brush I B and the primary brush l4 so as to form two load loops including a driving motor connected in each of the load loops between a primary brush and a secondary brush of the transformer primary and secondary brush sets.

A master controller I!) is provided for manually controlling the sequence of operation of the sys tem including controlling the driving motors H and I8 to provide either motoring, braking, or no torque to the vehicle axles. A separate source of electrical power supply including a battery 29 is provided for energizing the exciting coils of various relays arranged to control the operation of the system. switch 2| is provided for connecting and disconnecting the battery 20 to various parts of the system which are adapted to be energized by the battery. In most vehicles, it is desirable to pro In addition, a main control vide for the driving of the vehicle in forward and in reverse directions. This can readily be done in a vehicle propelled by electric motors by re versing the direction of the field excitation with respect to the armature to obtain two directions of rotation of the motors. In order to obtain this two-way rotation of the driving motors l1 and I8, a two-way switch 22 is adapted to contact terminals 23 and 24 to which motor controlling switches are connected. When the master controller I9 is in the off position and the control switch 2| is closed with the switch 22 closed on the contact 23, a circuit is formed impressing the voltage of the battery 20 across a main line relay exciting coil 25 through the control switch 2|, 5. set of contacts 26 of an overload relay 2! to the coil 25, and back to the other side of the battery 20. The energization of the coil 25 closes a circuit through a set of contacts 28 connected to the trolley or third rail shoe 29 arranged in contact with the supply line III. The closing of the contacts 28 connects the line In to the primary brush I3 of the rotary transformer I2 through a starting resistance 30, thereby impressing a reduced voltage across the primary brushes I3 and I4 of the rotary transformer, so as to minimize current surges when connecting the rotary transformer to the source of electrical power supply. The closing of the contacts 28 also impresses a voltage across an exciting coil 3| of a relay, the contacts of which are connected across the starting resistance 30, so that as the starting current taken by the rotary transformer decreases when the speed of the transformer increases and the drop across the starting resistance 30 correspondingly decreases, the voltage across the exciting coil 3| increases sufiiciently to energize the relay and close a circuit across the relay contacts 32, thereby short-circuiting the starting resistance 30 and applying full line voltage between the line In and ground across the primary brushes I3 and ll of the rotary transformer I2. With the relay contacts 28 and 32 closed, an exciting coil 33 of a polarized relay is connected directly across the source of electrical power supply between the line Ill and ground II, so as to energize a magnetic core 34 of the relay and attract a magnetic armature 35 thereof, as shown in the drawings, to close a circuit through a set of contacts 36 connected between the secondary brush I and an exciting coil 31 on the relay armature 35. This exciting coil 31 is adapted to energize the armature 35 of the polarized relay in such a direction as to maintain it in the position shown in the drawings under all conditions of operation wherein the voltage of the secondary brush it! does not fall below ground potential; that is, as long as the voltage between the primary brush i3 and the secondary brush I5 of the rotary transformer I2 does not exceed the voltage of the main source of electrical power supply.

In starting this type of power system, the main control switch 2| is closed and the master controller I9 is placed in its off position. Under these conditions, the circuits explained above are energized, and as explained in U. S. Patent 1,969,699. J. M. Pestarini, the voltage of the secondary brush I5 is the same as the voltage of the primary crush 53 and the voltage of the secondary brush it is the same as the voltage of the primary brush I4 when the primary brushes are first connected across the source of electrical power supply. Thus, it is not necessary to disconnect the driving motors from the brushes of the rotary transformer, as substantially no voltage is impressed across the motors I! and I8 under those starting conditions. Thus, when forward motion is desired, the switch 22 is closed upon the contact 23 to energize exciting coils 38 and 39 of switches 40 and M to complete a circuit from the primary brush I3 of the rotary transformer through contacts 42 of a deenergized short-circuiting relay through the driving motor II to a contact 43, a contactor 44, a motor series field exciting winding 45, a contactor 46, a contact 41, to the secondary brush I5 of the rotary transformer, and the motor I8 is connected to the secondary brush I6 of the rotary transformer through a relay contact 48, a contactor 49, a se ries field exciting winding 50, a contactor 5I,.contact 52, to the commutator of the driving motor I6, and through the contacts 53 of another shortcircuiting relay to the primary brush I l of the rotary transformer. The energizing coils 38 and 39 of the switches 40 and ll, respectively, are energized by the battery 20 and operate the switches 40 and 4|, respectively, to the positions shown in the drawings to provide the above circuits. In order to provide for a plurality of operating patterns, that is, to provide for a plurality of accelerating and decelerating curves, control field exciting windings 54 and 55 are arranged to provide a controlling component of excitation to the rotary transformer I2. These control field exciting windings are energized in accordance with the desired characteristics so as to vary the voltage between the primary and secondary brushes of the rotary transformer to control the voltage impressed upon the driving motors I1 and I8, and the energization of these control field exciting windings is supplied by auxiliary armature reaction excited dynamo-electric machines 56 and 51, respectively, of the type generally known as metadyne generators. These machines 56 and'51 are provided with sets of primary brushes 58 and 59 and 60 and 6|, respectively, which are short-circuited to provide a substantially constant potential across these brushes of zero value. These auxiliary dynamo-electric machines 56 and 51 are adapted to induce a voltage across sets of secondary brushes 62 and 63 and 64 and 65 thereof. These respective sets of secondary brushes are connected across the field exciting windings 54 and 55 and provide an energization thereto which varies in accordance with the desired operating characteristics of the rotary transformer. In order to obtain these field exciting winding energizing voltages, the auxiliary machines 56 and 51 are provided with a plurality of field exciting windings to provide various components of excitation to these machines, and these various components of magnetic excitation are composed or combined within these auxiliary machines. By thus combining a plurality of components in small auxiliary machines, it is possible to obtain a more rapid response by controlling relatively small values of electric current.

In order to obtain this desired excitation for the auxiliary composing dynamo-electric machines 56 and 51, a pattern dynamo-electric machine 66 is provided which is adapted to energize field exciting windings of the composing auxiliary dynamo-electric machines and is arranged to provide different voltage characteristics for energizing the field exciting windings in accordance with the different positions of the master controller I9. This pattern dynamoelectric machine 66 is provided with two substantially magnetically independent exciting systems constructed so as to saturate magnetically at low values of excitation. A field exciting winding 61 is connected to the primary brush l3 and the secondary brush l of the rotary transformer l2 so that its energization varies in accordance with the voltage across the driving motor I! and is arranged on one of these magnetic excitation systems, and a second field exciting winding 98 is provided on the other excitation system and is connected to the primary brush l4 and the secondary brush l5 of the rotary transformer 62, so that its energization varies inversely with respect to the voltage across the driving motors. The components of voltage which would be generated by the pattern exciter 66 dueto the respective field exciting windings 61 and 69 are represented by curves A and F of Figs. 2 and 3, respectively. A third field exciting winding 69 is arranged to provide a component of excitation to the pattern dynamo-electric machine 66 in opposition to the excitation of the field exciting winding 61 and is adapted to be connected across the battery 29 through a series of resistance steps '19, H, and i2 and a fixed resistor 19. The variable resistance steps ID, H and F2 are adapted to be shunted out of the circuit through contacts on the master controller. The resultant component voltages produced by the various energizations of the field exciting winding 69 and the winding 61 are represented by the curves B, C, D, and E of Fig. 2. A fourth field exciting winding 14 is arranged to provide another component of excitation to the pattern dynamo-electric machine 66 in opposition to the excitation of the field exciting winding 68 and is connected to contacts I 5 and I6 of the master controller through which it is adapted to be connected through a series of variable resistance steps 11, 18, and I9, and a fixed resistance 99 across the battery 20. In addition to varying the energization of the field exciting winding 14 by the master controller through the variable resistance steps 11, I8, and 19, the contacts 15 and I6 arearranged to be energized through contactors of the master controller so that the energization of the field exciting winding H also may be reversed in direction for emergency braking operating conditions of the motors as controlled by the master controller l9. The resultant component voltages produced by the various energizations of the field exciting winding 14 and the winding 69 are represented in Fig. 3 by the curves G. H, J and K for motoring and regenerative braking and by curve L for emergency dynamic braking. The total or net voltage generated by the pattern dynamo-electric machine exciter 66 is the sum of the component voltages represented by the curves in Figs. 2 and 3. Since the field exciting windings 69 and II are never completely deenergized, there is no net voltage corresponding to curves A and F'. Furthermore, the voltages applied to the field exciting windings 61 and 68 are complementary, that is, as the voltage across one increases, the voltage across the other decreases correspondingly, the algebraic sum of these two voltages being equal to the transformer primary voltage across the brushes i3 and it. Thus, the total or net generated voltage of the pattern exciter 66 may be represented in Fig. 4 by curves M, N, P, and R for motoring and regenerative braking and by curve S for emergency dynamic braking. Curve R. also represents the voltage characteristic for the off" position of the master controller 59. The energization provided by this pattern dynamo also is arranged to be varied by a series of steps of resistance 9!, 92, 93, and 94 connected to contacts on the master controller I9 and to field exciting windings 95 and 99 on the auxiliary composing dynamo-electric machines and 51, respectively. These field exciting windings 95 and 86 are adapted to be connected to the pattern dynamo-electric machine 65 through the master controller and its associated resistances, through the contactors 8'! and 88 and contacts 89 and 99 of a switch 9|, contacts 92 of an under voltage relay, and through contacts 99 of the main control relay. The energization of these field exciting windings and 89 is adapted to be reversed for motoring and braking operating conditions by the switch 91. This switch is controlled by a pair of operating coils 94 and 95 which are energized by the battery 20 through contacts 96 and 91 on the master controller I9 for actuating the switch 9! to the position shown in the drawings for motoring operation of the driving motors, or for actuating the switch 9| to reverse the connections of the field exciting windings 85 and 96 when the master controlleris in the olP or braking positions. The energization of these windings is determined by the current output patterns of the exciter 66 and is related to the voltage patterns of Fig. 4 by the resistance of the load circuit. These current patterns are represented in Fig. 5 by curves T, U, V, and W for motoring and regenerative braking, curve X for the oil position of the controller l9, and curve Y for emergency dynamic braking.

It also is desirable that the speed of the rotary transformer l2 should be maintained substantially constant at a predetermined value to obtain the desired transformer action. This may be obtained by regulating a component of excitation of the machine by any suitable speed responsive device, so as to increase or decrease the input to the transformer to maintain substantially constant speed. In the illustrated arrangement, an auxiliary generator 98, regulated at substantially constant voltage, is arranged in parallel with an unsaturated auxiliary generator 99 and connected thereto, so that the voltages of the two auxiliary generators 99 and 99 are substantially equal and opposite when the rotary'transformer l2 operates at its predetermined desired speed. These two generators 99 and 99, as well as the auxiliary metadyne generators 59 and 51 are mechanically drivenby the rotary transformer I2 in.a predetermined speed relationship with respect to the speed thereof. The unsaturated auxiliary generator 99 is provided with a shunt field exciting winding thereof, so that its excitation varies in accordance with the voltage and the speed of the generator 99, and thereby provides a large variation in the voltage across the generator 99 for, any given change in speed thereof. The auxiliary generator 99 is provided with a field exciting winding Ml which also is adapted to be connected across the terminals of the generator 98, but this field exciting winding is arranged to pro vide an excitation to this machine such that. over a very wide range of speed, the generator 98 will provide a substantially constant voltage. These two generators are connected across a field exciting winding I92 on the auxiliary exciter 51 and a field exciting winding H13 on the auxiliary exciter 56. Since the voltages of the two auxiliary generators 98 and 99 are substantially equal and opposite at the desired operating speed of the rotary transformer Hi, the field exciting I09 connected across the terminals windings I02 and I03 are not energized when the rotary transformer is operating at its desired substantially constant speed. However, if the load on the rotary transformer increases such that its speed decreases, the voltage of the auxiliary generator 99 decreases very rapidly and the difference between its voltage and that of the substantially constant voltage auxiliary generator 98 impresses a potential across the field exciting windings I02 and I03, so as to excite auxiliary exciters and 59 to produce an energization of the field exciting windings 55 and 54, respectively, which will tend to increase the input to the rotary transformer I2 and restore its speed to normal operating conditions. 0n the other hand, as the speed of the rotary transformer increases above a predetermined desired value, the

voltage of the auxiliary generator 99 will exceed that of the substantially saturated generator 99 and cause a current to fiow in the opposite direction through the field exciting windings I03 and I02, such that the voltage impressed across the field exciting windings 54 and 53 will energize these field exciting windings of the rotary transformer so as to decrease the speed thereof until the voltages of the auxiliary generators 98 and 99 again are substantially equal. In order to insure that the voltage of the auxiliary generator 98 remains substantially constant, a voltage regulator is provided which includes an exciting coil I04 connected across the terminals of the auxiliary generator 98 such that the field exciting winding IOI of this generator is connected thereacross through contacts I05. However, if the voltage across the generator 90 exceeds a predetermined value, the exciting coil I04 of the voltage regulator energizes the armature I06 thereof so as to close a circuit through a pair of contacts I01 and place the field exciting winding IOI across a pair of resistances I08 and I09 which will decrease the energization of the field exciting winding IOI and reduce the voltage of the auxiliary generator 98.

In order to keep the battery fully charged,

the auxiliary generator 98 also is used as a battery charging generator. One terminal of the generator 98 is connected directly to the terminal of the battery 20 with the voltage of the generator in opposition to that of the battery, and the other terminal of the generator is connected to the other terminal of the battery through a pair of contacts H0 and another pair of contacts III through a reverse current relay' II2 having a pair of contacts I I3. When the voltage of the generator 98 is such as to charge the battery 20, a current fiows from the generator through an exciting coil II4 of the reverse current relay II2, so as to close a circuit through the relay contacts H3 and impresses the voltage of the generator 98 across the battery 20'. Should the voltage of the generator 98 fall below the voltage of the battery 20, an exciting coil II5 of the relay I I2 will be energized by current flowing from the battery to the generator 98, so as to oppose the excitation of the exciting coil I I0 and deenergize the armature of the reverse current relay II2, so as to open the circuit through the contacts II3, thereby preventing the reverse fiow of current and discharge of the battery -20 through the auxiliary generator 98.

Under certain conditions of operation, the overload on the rotary transformer I2 may become excessive, so that the speed regulating arrangement including the auxiliary generators 99 and 99 may not be adequate to provide the desired speed regulation. In order to insure against damage due to excessive overloads, the overload relay 2! is provided with an energizing coil II9 which is connected in series with the field exciting windings I 02 and I03 in circuit with the auxiliary speed regulating generators 98 and 99, so that if the overload on the rotary transformer I2 is such as to reduce the speed thereof below a predetermined value, the overload relay exciting coil II 6 becomes sufficiently energized so as to operate the relay to open the contacts 26 and deenergize the exciting coil 25 of the main line relay. This opens the main line contacts 28 of the relay, thereby disconnecting the entire system from the main source of electrical power supply I0. A holding coil III is arranged on the overload relay 21, so that when the relay is operated by the exciting coil II6 to disconnect the system from the main source of electrical power supply, the circuit of the exciting coil II! is closed through a set of contacts II8 of the overload relay 21 across the battery 20. Thus, the system becomes inoperative under heavy loads until the overload relay 21 is reset by opening the main control switch 2| to dcenergize the holding coil II! of the overload relay, and then reclosing the main control switch 2|.

Under certain other operating conditions, the voltage across the primary brushes I3 and I4 of the rotary transformer I2 may fall below a pre determined value, so that the system no longer can operate as desired. This may result from a short circuit on the main source of electrical power supply or from a loss of line voltage due to a break in the connection between the contactor trolley Or shoe 29 and the trolley wire or third Tail I0. Under these conditions, it is desirable that the auxiliary load which is driven by the rotary transformer I2 should be removed therefrom and an under-voltage relay H9 is arranged to control this operation. With the master controller in the oiT position, an exciting coil I20 of the under-voltage relay II 9 is cOnnected across the main source of electrical power supply I0 through the relay contacts 28 and 32 and to ground through a contact I2I' and two interconnected fingers I22 and I23 and contact I24, all Ofthe master controller I9. Energizetion of the exciting coil I 20 operates the undervoltage relay so as to close a set of contacts I25 and provide a holding circuit for the exciting coil I20 for all positions of the master controller. In this position, the under-voltage relay also opens a circuit through a set of contacts I26 connected in series with an exciting coil I21 arranged to energize an unloading relay including the contacts 92, H0, and III. When the exciting coil I21 is thus deenergized, the circuits through the contacts 92, H0 and III are closed, thereby placing an auxiliary load upon the rotary transformer I2. If the master controller I9 is turned to motoring or off positions and the voltage across the primary brushes I3 and I4 of the rotary transformer I2 should fall below a predetermined value for any of the reasons such as those indicated above, the exciting coil I20 is not sufficiently energized to hold the under-voltage relay H9 in a position to close the circuit through the contacts I25, and the contactors of this relay then will close a circuit through the contacts I26 so as to energize the exciting coil I21 of the unloading relay. This will cause the unloading relay to open the circuits through the contacts 92, I00, and III, so as to deenergize the field exciting windings 8'5 and 06 of the composing exciter generators 56 and 51 and also open the circuit between the auxiliary generator 93, the battery 20, and the auxiliary generator 99 through the field exciting windings I02 and I03,

, thereby removing all of the auxiliary load which is supplied by auxiliary machines driven by the rotary transformer I2. With the master controller I9 in braking position, this operation is prevented by opening the power supply to connected across the brushes of the rotary transformer, it is necessary that the voltage across the motors be reduced to zero, and this can be provided by reducing the voltage of the pattern exciter 66 substantially to zero by actuating the switch 9| to its braking position by energizing the coil 95 from contact 96 of the master controller I9 and the output of the pattern exciter 66 also is reduced substantially to zero, as indicated by curve X in Fig. 5. This results in the voltage of brush I5 becoming the same as that of the brush I3 and the voltage of the brush I6 the same as that of brush I4, as has been explained above, so that substantially no current flows through the armatutre and the series field exciting windings 45 and 50 of the driving motors I1 and I8, respectively. The motors I1 and III also are provided with separately excited field exciting windings I28 and I29 connected across an auxiliary armature reaction excited generator I30 and slight fluctuations in the main supplyline voltage might produce torque in the drivin motors I1 and I8 if these separately excited field exciting windings I28 and I29 are energized. In order to insure against the excitation of the driving motors by these separately excited field exciting windings, a relay having contacts "I is provided 'for controlling the energization of a control field exciting winding I32 on the motor field exciter I30. This field exciting winding I32 is adapted to be energized by the pattern dynamo-electric machine 56, so that the excitation of the separately excited field exciting windings I28 and I29 of the motors will vary in accordance with the variation of the voltage generated by the pattern dynamo-electric machine 66. The relay contacts I3I are adapted to be closed under all conditions of operation, except when the master controller is in the oil position, under which conditions, an exciting coil I33 is arranged to be energized from the battery through a contact I34, a finger I35, electrically connected to a finger I36 and a contact I31, all of the master controller, so as to operate the relay and open the circuit between the contacts I3I, thereby deenergizing the field exciting winding I32. This deenergization of the field exciting winding I32 of the motor exciter I30 results in the deenergization of the separately excited field exciting windings I28 and I29 of the motors so that substantially no torque will be developed by the motors. The excitation of the separately excited motor field exciting windings I28 and I29 also is reversed relatively to the motor armatures for reverse motor operation and is controlled by the same direction control switch 22 which controls the relative connections of the series field exciting windings. If the switch 22 is closed upon the contact 23, the switch operating coils 38 and 39 are energized, so as to operate the switches 40 and 4|, respectively, as shown in the drawings. Furthermore, this energizes an operating coil I38 0! a switch I 39, so as to actuate this switch to energize the field exciting winding I32 of the motor field exciter I30 by the pattern dynamoelectric machine 66 through contactors I40 and I which can be in circuit through contacts I42 and I43. If it is desired to have the driving mo-, tors operate in the reverse direction, the main control switch 22 is closed upon the contact 24, so as to energize an operating coil I44 of the switch I39 to actuate this switch and close the contactor I" on a contact I45 and close the contactor I40 on the contact I43, thereby reversing the energization of the field exciting winding I32 of the motor field exciter I30. This reverses the energization of the motor field exciting winding I28 and I29 and thereby reverses the excitation provided by these field exciting windings with respect to the motor armatures I1 and I8. Furthermore, switch operating coils I46 and I41 of the switches 40 and H are energized so as to operate the switches 43 and H to close the con- .tactor 44 on a contact I48, contactor 46 on contact 43, contactor 49 on contact 52, and a contactor M on a contact I49, thereby reversing the energization of the field exciting windings 45 and 50, respectively. Thus, when the direct control switch 22 is closed upon the contact 24, all of the field exciting windin s of the motors are reversed with respect to the armatures of the motors and a reverse rotation is provided. In

order to obtain an accelerating or motoring torque from the motors I1 and I8, the master controller I9 is arranged to be operated, so that the pattern dynamo-electric machine 66 will provide the desired excitation to the auxiliary exciter dynamo-electric machines 56 and 51 in order to control the energization of the field exciting windings 54 and 55 to impress the desired voltage upon the driving motors. The excitation of the transformer exciters 56 and 51 is controlled by a plurality of fingers I50 of the master controller I! which is adapted to contact a corresponding plurality of contacts I5I to 'vary the resistance connected in series with the field exciting windings 85 and 36 of the transformer exciters 56 and 51. The excitation of the control fields and 36 of the transformer exciters also is varied by controlling the excitation of the pattern dynamo-electric machine 56 by a plurality of fingers I52 which is arranged to engage contacts I53 to vary the resistance in series with the field exciting winding 14 on the pattern dynamoelectric machine 66. The circuit on the field ex citing winding 14 is completed through contacts 15 and 16 arranged to be engaged by fingers I56 and I51 and through a finger I58 arranged to engage a contact I59 of the master controller I9. Furthermore, the excitation of the pattern dynamo-electric machine 66 is varied by a plurality oi fingers I54 arranged to engage a plu-- rality of contacts I55 to vary the resistance in series with the field exciting winding 69 of the pattern dynamo-electric machine 66.

For all motoring positions of the master controller I9, the fingers I22 and I23 engage the contacts I21 and I24 to provide for the energization of the under-voltage relay exciting coil I20. During motoring operation of the system, the exciting coil I33 of the relay which controls the energization of the motor field exciting winding I32 is adapted to be deenergized, while the fin:

ger I36 is adapted to engage the contact I31 and is electrically connected to a finger I60 arranged to engage a contact. I6I to complete the circuit of the unloading relay exciting coil I21 across the battery 20. The finger I36 also is electrically connected to a finger I62 arranged to engage contact 81 to energize the operating coil 84 of the switch 8|, as explained above.

With this type system, it is desirable that the traction motors be adapted to provide a retarding or braking force to assist in stopping the vehicle. For this purpose, the master controller I8 is provided with four braking positions and an additional emergency braking position. Under normal braking conditions, the master controller may be moved to any of its four normal braking positions to vary the rate of deceleration of the vehicle by varying the energization of the rotary transformer control field exciting windings 54 and 55. The energization of these field exciting windings for braking purposes is reversed by energization of the coil 85 of the switch 9| through master controller contact 86,

fingers I81 and I36, and contact I31, so that switch contactor 81 engages contact 80 and contactor 88 engages contact I88 and is varied by varying the energization of the control field exciting windings 85 and 86 of the transformer exciters 56 and 51 by varying the resistance in series with these field exciting windings through a plurality of fingers I63 arranged to engage the contacts I5I connected across the resistances 8I to 84 inclusive. Furthermore, the energization of the control field exciting windings 85 and 86 is varied by varying the excitation of the pattern dynamo-electric machine 66 in the same manner as the excitation of this machine is varied for motoring purposes. In the emergency braking position of the master controller I8, all or the resistance in series with the field exciting windings 85 and 86 of the transformer exciters is short-circuited through the fingers I63 and the contacts I5I and the excitation of the field exteristic as shown by curve Y of Fig. 5. Under normal operating conditions when braking, the motors I1 and I8 will remain connected across the brushes of the rotary transformer I2 which operates to generate a voltage slightly in excess of the voltage of the main source of electrical power supply In to provide regenerative braking. This condition will remain satisfactory for regenerative braking providing the voltage of the driving motors does not exceed the voltage of the electrical power supply by too great a value; that is providing the voltage of the driving motors does not exceed by too great a value the voltage impressed by the line I0 across the primary brush and the secondary brush to which these motors are connected. It is quite possible, however, that the voltage generated by the traction motors may exceed this predetermined value, as this voltage is dependent on the vehicle speed and the excitation of the motor as determined by the mastercontroller I8. In order to maintain the stability of the system, it is desirable to provide an emergency load absorbing device which may be connected between the traction motor and the brush of the rotary trans former, so as to reduce the voltage impressed by the motor across the brushes of the transformer. This over-voltage condition will result durin braking when the vehicle is traveling above a predetermined speed; The polarized relay also will operate to close contacts I68 and HI any time the potential of brush I5 falls below that of brush I4, whether during acceleration or braking. However, coils I12 and I13 may be energized only when contact I82 engages contactor segment I63, that is, only for a braking position ,of the master controller I8. During braking, if the potential of the secondary brush I5 becomes lower than the potential of the primary brush I4, the current through the exciting coil 31 of the polarized relay will be reversed in direction and the armature 35 will be actuated in the opposite direction from that shown in the drawings. when in this position, the polarized relay closes a circuit through contacts I68, so as to energize an exciting coil I18 on the polarized relay armature 35 to maintain the relay in this position as long as the voltage of the secondary brush I6 remains above the voltage of the primary brush H. In this position, the polarized relay also closes a circuit throu contacts I1I, so as to energize relay coils I12 and I13 and thereby open the circuits through the contacts 53 and 42, inserting emergency braking resistances I14 and I15 between the driving motors I8 and I1, respectively, andthe brushes of the rotary transformer I2. When these emergency braking resistances are inserted in series with the motors, the voltage of the motors impressed across the brushes of the rotary transformer is decreased to a value below that of the main source of electrical power supply. After this operation of the polarized relay and during the reduction of speed during braking, the potential or brush I6 falls below that of brush I4. Thereupon, the polarized relay again returns to the position shown in Fig. 1, and opens contact HI and deenergizes coils I12 and I13, cutting out the emergency braking resistors I14 and I15 from the motor circuits.

Under certain circumstances, as when contact may be lost between the power system and the source of electrical power supply as the trolley or shoe 28 becomes disconnected from the trolley wire or third rail III or when a short-circuit occurs across the source of electrical power supply, it-is desirable that a braking force may still be obtained by use of the traction motors acting as generators. Under these conditions, dynamic braking is provided by connecting a main load absorbing resistor I16 across the primary brushes I3 and I4 of the rotary transformer I 2. This connection of the main load absorbing resistor I16 is obtained by closing a set of contacts I11 by a relay, the exciting coil I18 of which is energized under emergency braking conditions through the master controller contact I68, finger I61, finger I36, and contact I31. Under other braking conditions, the exciting coil I18 is connected across the battery 26 through a set of contacts I18 of the under-voltage relay H8 or through another set of contacts I88 of an overvoltage relay I8I. The circuit through the under-voltage relay H8 is completed through a contact I82 and a finger I83 of the master controller, which is electrically connected to the finger I36 arranged to engage contact I31 connected to the battery 20. The contacts I19 of the under-voltage relay are closed whenever the voltage of the main source of electrical power supply falls below a predetermined value, so that the circuit will be closed through these contacts under this condition. Furthermore, if contact with the main source of electrical power supply is lost, the voltage which the motors will impress across the primary brushes of the rotary transformer I2 will exceed a predetermined value and a holding coil I84 of the over-voltage relaywill maintain closed the circuit through the contacts I80 of this relay. The over-voltage relay I8I is operated by an exciting coil I85 which is energized by the voltage between primary brushes I3 and I4 of the rotary transformer I2. When this exciting coil I85 is energized above a predetermined value, it actuates the'over-voltage relay, so as to close a set of contacts I88 which completes a circuit through a holding coil I84, which thereafter maintains closed the contacts of the over-voltage relay for all operating conditions of the power system until such a time as the master controller is turned to the "01? or any motoring position. With this relay closed,

, the main load absorbing resistor relay excitin coil I18 circuit is closed across the batte y 20 during braking through the contacts I80 of the over-voltage relay and the master controller contact I82, fingers I83 and I36, and contact I31.

Thus, it is seen that we have. provided a power system wherein gradual acceleration of the driving motors may be provided in opposite directions by a master'controller and associated control circuits, and gradual electric braking also may be controlled by the master controller and its associated circuits through the driving motors irrespective of whether or not the system is connected to the main source of electrical power supply, so that the operator may obtain a smooth operation of the power system under all varyin load conditions While we have illustrated and described a particular embodiment of our invention, modifications thereof will occur to those skilled in the art. We desire it to be understood, therefore, that our invention is not to be limited to the particular arrangement disclosed, and we intend in the appended claims to cover all modifications which do not depart from the spirit and scope of our invention.

What we claim as new and desire to secure by Letters'Patent of the United States, is:

1. In a control system for an electric vehicle, the combination of an armature reaction excited rotary transformer having a commutator and sets of primary brushes and secondary brushes displaced with respect to each other about said commutator, a driving motor, means for connecting said driving motor across a brush of said primary brushes and a brush of said secondary brushes, a main load absorbing braking resistance, control means for connecting said resistance in series circuit with said primary brushes 1 to establish dynamic braking operation,an emergency braking resistance, means for connecting said emergency braking resistance in series circuit with said motor, and means dependent on the speed of said motor for controlling the amount of said resistances connected in series circuit with said motor when said control means is operated to" establish dynamic braking operation.

2. A power system including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes, means for connecting said primary brushes across said source of electrical power supply, an B-connected motor load on said transformer, an emergency electrical load absorbing means including an emergency braking resistor, means for inserting and removing said emergency load absorbing means in circuit with said motor load between said motor load and said transformer, a main electrical load absorbing means including a main load resistor, means in circuit with said main load absorbing means for connecting said main load absorbing means across said primary brushes, and means dependent on the electrical potential across said primary brushes for opening and closing the circuit of said main load absorbing means circuit connecting means.

3. A power system including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes, means for connecting said primary brushes across said source of electrical power supply, a pair of driving motors, means for said one of said motors between said motor and said dynamo-electric transformer brushes, a main electrical load absorbing means including a main load resistor, means in circuit with said main load absorbing means for connecting said main load absorbing means across said primary brushes, and means dependent on the electrical potential across said primary brushes for opening and closing the circuit of said main load absorbing means circuit connecting means.

4. A power system including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes, means for connecting said primary brushes across .said source of electrical power supply, means including a starting resistance for reducing current surges when said transformer primary brushes are connected by said last-mentioned means to said source of electrical power supply, means dependent upon the voltage across said primary brushes for automatically short-circuiting said starting resistance,, a pair of driving motors, means for connecting one of said driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means for connecting the other of said driving motors across the other brush of said pair of primary brushes and the other brush of said pair of secondary brushes. an emergency electrical load absorbing, means including an emergency braking resistor, and.

moving said emergency load absorbing means in circuit with said one of said motors between said motor and said dynamo-electric transformer brushes.

5. A power system including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes, means for connecting said primary brushes across said source of electrical power supply, a pair of driving motors, means 101 connecting one of said driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means for connecting the other of said driving motors across the other brush of said pair of primary brushes and the other brush of said pair of secondary brushes, means for controlling the rate of acceleration of said driving motors, an emergency electrical load absorbing means including an emergency braking resistor, means for inserting and removing said emergency load absorbing means in circuit with said one of said motors between said motor and said dynamo-electric transformer brushes, a main electrical load absorbing means includin a main load resistor, means in circuit with said main load absorbing means for connecting said main load absorbing means across said primary brushes, and means dependent on the electrical potential across said primary brushes for opening and closing the circuit of said main load absorbing means circuit connecting means.

6. A power system including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes, means for connecting said primary brushes across said source of electrical power supply, a pair of driving motors, means for connecting one of said driving motors across a brush of said primary brushes and a brush former brushes, a main electrical load absorbing means including a main load resistor, means in circuit with said main load absorbing means for connecting said main load absorbing means across said primary brushes, and means dependent on the electrical potential across said primary brushes for opening and closing the circuit of said main load absorbing means circuit connecting means.

7. A power system including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes, means for connecting said primary brushes across said source of electrical power supply, a pair of driving motors, means for connecting one of said driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means for connecting the other of said driving motors across the other brush of said pair of primary brushes and the other brush of said pair of secondary brushes, means including a control field exciting winding on said transformer for controlling the power output of said transformer, an emergency electrical load absorbing means including an emergency braking resistor, means for inserting and removing said emergency load absorbing means in circuit with said one of said motors between said motor and said dynamo-electric.

transformer brushes, a main electrical load absorbing means including a main load resistor means in circuit with said main load absorbing means for connecting said main load absorbing means across said primary brushes, and means dependent on the electrical potential across said primary brushes for opening and closing the circuit of said main load absorbing means circuit connecting means.

8. A power system including a source of electrical power, supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes, means for connecting said primary brushes across said source of electrical power supply, a pair of driving motors, means for connecting one of said driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means for connecting the other of said driving motors across the other brush of said pair of primary brushes and the other brush of said pair of secondary brushes, a field exciting winding for said transformer, means including an auxiliary dynamoelectric machine arranged to energize said transformer field exciting winding for controlling the rate of acceleration of said driving motors, an emergency electrical load absorbing means including an emergency braking resistor, means for inserting and removing said emergency load absorbing means in circuit with said one of said motors between said motor and said dynamo-electric transformer brushes, a main electrical load absorbing means including a main load resistor, means in circuit with said main load absorbing means for connecting said main load absorbing means across said primary brushes, and means dependent on the electrical potential across said primary brushes for opening and closing the circuit of said main load absorbing means circuit connecting means.

9. A power system including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes, means for connecting said primary brushes across said source of electrical power supply, means including a starting resistance for reducing current surges when said transformer primary brushes are connected by said last-mentioned means to said source of electrical power supply, means dependent upon the voltage across said primary brushes for automatically short-circuiting said starting resistance, a pair of driving motors, means for connecting one of said driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means for connecting the other of said driving motors across the other brush of said pair of primary brushes and the other brush of said pair of secondary brushes, an emergency electrical load absorbing means including an emergency braking resistor, means for inserting and removing said emergency load absorbing means in circuit with one of said motors between aid motor and said dynamo-electric transformer brushes, a main, electrical load absorbing means including a main'load resistor, means in circuit with said main load absorbing means for connecting said main load absorbing means across said primary brushes, and means dependent on the electrical potential across said primary brushes for opening and closing the circuit of said main load absorbing means circuit connecting means.

10. A power system including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes, means for connecting said primary brushes across said source of electrical power supply, a pair of driving motors, means for connecting one of said driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means for connects ing the other of said driving motors across the other brush of said pair of primary brushes and the other brush of said pair of secondary brushes, means dependent on the load on said transformer for disconnecting said primary brushes from said source of electrical power supply, a main control circuit breaker arranged to make and break all of the control circuits of said power system, an emergency electrical load absorbing means including an emergency braking resistor, means for inserting and removing said emergency load ab-'- sorbing means in circuit with said one of said motors between said motor and said dynamoelectric transformer brushes, a main electrical load absorbing means including a main load resistor, means in circuit with said main load absorbing means for connecting said main load absorbing means across said primary brushes, and means dependent on the electrical potential across said primary brushes for opening and closing the circuit of said main load absorbing means circuit connecting means.

11. A power system including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes, means for connecting said primary brushes across said source of electrical power supply, a pair of driving motors, means for connecting one of said driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means for connecting the other of said driving motors across the other brush of said pair of primary brushes and the other brush of said pair of secondary brushes, an auxiliary dynamo-electric machine for controlling the rate of acceleration of said driving motors, an emergency electrical load absorbing means including an emergency braking resistor, means for inserting and removing said emergency load absorbing means in circuit with said one of said motors between said motor and said dynamo-electric transformer brushes, a main electrical load absorbing means including-a main load resistor, means in circuit with said main load absorbing means for connecting said main load absorbing means across said primary brushes, means dependent on the electrical potential across said primarybrushes for opening and closing the circuit of said main load absorbing means circuit connecting means, an auxiliary electric generator mechanically driven by said dynamo-electric transformer, an auxiliary electrical load, and means dependent on the electrical potential across said primary brushes for connecting and disconnecting said auxiliary electrical load to said auxiliary generator.

12. A power system including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes, means for connecting said primary brushes across said source of electrical power supply, means including a starting resist ance for reducing current surges when said transformer primary brushes are connected by said last-mentioned means to said source of electrical power "supply, means dependent on the voltage across said primary brushes'for automatically short-circuiting said starting resistance,. a pair of driving motors, means for connecting one of said driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means for connecting the other of said driving motors across the other brush of said pair of primary brushes and the other brush of said pair of secondary brushes, means for remotely controlling the direction of rotation of said driving motors, an emergency electrical load absorbing means including an emergency braking resistoiymeans for inserting and removing said emergency load absorbing means in circuit with one of said motors between said motor and said dynamo-electric transformer brushes, a main electrical load absorbing means including a main load resistor, means in circuit with said main load absorbing means for connecting said main load absorbing means across said primary brushes, and means dependent on the electrical potential across said primary brushes for opening and closing the circuit of said main load absorbing means circuiting connecting means.

13. A power system including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary-brushes electrically displaced from said primary brushes, means for connecting said primary brushes across said source of electrical power supply, a pair of driving motors, means for connecting one of said driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means for connecting the other of said driving motors across the other brush of said pair of primary brushes and the other brush of said pair of secondary brushes, means dependent on the speed of said transformer for controlling the power output thereof, an emergency electrical load absorbing means including an emergency braking resistor, means for inserting and removing said emergency load absorbing means in circuit with said one of said motors between said motor and said trical load, and means dependent on the electrical potential across said primar'y'brushes for connecting and disconnecting saidauxiliary electrical load to said auxiliary generator.

14. A power system including a source of electrical power supply, an armature'reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes means for connecting said primary brushes across said source of electrical power supply, a pair of driving motors, means for connecting one of said driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means for connecting the'other of said driving motorsiary armature reaction excited dynamo-electricmachine arranged to energize said control field exciting winding, an emergency braking resistor, means for inserting and removing said emergency load absorbing means in circuit with said'one of said motors between said motor and said dynamoelectric transformer brushes, a main electrical load absorbing means including-a main load resistor, means in circuit with said main load absorbing means for connecting said main load abfrom said primary brushes, means for connecting said primary brushes across said source of electrical power supply, a pair of driving motors, means for connecting one of said driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means 'forconnecting the other of ,said driving motors across the other brush'of said pair of primary brushes and the other brush of said pair of sec- 'ondary brushes, means for controlling the rate of acceleration and the rate of braking of said driving motors, an emergency electrical load absorbing means including an emergency braking resistor, means for inserting and removing said emergency load absorbing means'in circuit with said one of said motors between said motor and said dynamo-electric transformer brushes, a main electrical load absorbing means including a main load resistor, means in circuit with said main load absorbing means for connecting said main load absorbing means across said primary sorbing means across said primary brushes, means dependent on the electrical potential across said primary brushes for opening and closing the circuit of said main load absorbing means'circuit connecting means, an auxiliary electric generatormechanically driven by said" dynamo-electric transformer, an auxiliary electrical load, and means dependent on the electrical potential across said primary brushes for connecting and disconnecting said auxiliary electrical load to said aux- .iliary generator.

15. A po'wersystem including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a brushes, means dependent on the electrical potential across said primary brushes for opening and closing the circuit of said main'load absorbing means circuit connecting means, an auxiliary electricgeneratormechanically driven by said dynamo-electric transformer, an auxiliary electrical load; and means dependent on the electrical potential-across saidprimary brushes for conpair of secondary brushes electrically displaced from said primary brushes,'means for connecting said primary brushes across said source of electrical power supply, a pair of driving motors, means for connecting one of said'driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means for connecting the other of said driving motors across the other brush of said pair of primary brushes and the other brush of said pair of secondary brushes, a control field exciting 'winding for said transformer, means including an auxiliary armature reaction excited dynamo-electric machine arranged to energize said control field exciting winding, means dependent on the speed of said transformer for controlling the voltage of said auxiliary dynamo-electric machine, an emergency electrical load absorbingmeans in cluding an emergency braking resistor, means for inserting and removing said emergencyload necting and disconnecting said auxiliary electricalload to said auxiliary generator. 1

' I 17. 'A- power system including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes, means for connecting said primary brushes across said source of electrical power supply, a pair of driving motors, means for connecting'one of said driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means for connecting the other of said driving motors across the other brush of said pair of primary brushes andthe other brush of said pair of secondary brushes, means dependent on the load on said transformer for disconnecting said primary brushes from said source of electrical power supply, an emergency braking resistor, means for insertingandremoving said emergency braking resistor in circuit with said one of said motors between said motor and said dynamo-electric transformer brushes, a main electrical load absorbing means including a main load resistor, means in circuit with said main load absorbing means for connecting said main'load absorbing means across said primary brushes, means dependent on the electrical potential across said primary brushes for opening and closing the circuit of said main load absorbing means circuit trical ower'supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes, means for connecting said primary brushes across said source of electrical power supply, a pair of driving motors, means for connecting one of said driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means for connecting the other of said driving motors across the other brush of said pair of primary brushes and the other brush of said pair of secondary brushes, means dependent on the load on said transformer for disconnecting said primary brushes from said source of electrical power supply, a main control circuit break'er arranged to make and break all of the control circuits of said power system, said load dependent means includinga relay arranged to maintain disconnected said primary brushes from said source of electrical to open all of the control circuits and is reclosed, a main electrical load absorbing means including a main load resistor, means dependent on the electrical potential across said primary brushes for connecting said main load absorbing means across said primary brushes, an auxiliary electric generator mechanically driven by said dynamo-electric transformer, an auxiliary electrical load, and means dependent on the electrical potential across said primary brushes for connecting and disconnecting said auxiliary electrical load to said auxiliary generator.

19. A power system including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a commutator with a pair of primary brushes and a pair of secondary brushes electrically displaced from said primary brushes, means for connecting said primary brushes across saidsource of electrical power supply, means including a starting of said pair of primary brushes and the other brush of said pair of secondary brushes, an emergency electrical load absorbing means including an emergency braking resistor, means for inserting and removing said emergency load absorbing means in circuit with said one of said motors between said motor and said dynamoelectric transformer brushes, a main electrical load absorbing means including a main load resistor, means in circuit with said main load absorbing means for connecting said main load absorbing means across said primary brushes, means dependent on the electrical potential across said primary brushes for opening and closing the circuit of said main load absorbing means circuit connecting means; an auxiliary electric generator mechanically driven by said dynamo-electric transformer, an auxiliary electrical load, and means dependent on the electrical potential across said primary brushes for connecting and disconnecting. said auxiliary electrical load to said auxiliary generator.

20. A power system including a source of electrical power supply, an armature reaction excited dynamo-electric transformer having a com mutator witha pair of primary brushes and a pair of secondary brushes electrically displaced from said primary'brushes, means for connecting said primary brushes across said source of electrical power supply, a pair of driving motors,

means for connecting one of said driving motors across a brush of said primary brushes and a brush of said secondary brushes, other means for connecting the other of said driving motors across the other brush of said pair of primary brushes and the other brush of said pair of secondary brushes, a field exciting winding for said rotary transformer, an auxiliary dynamo-electric machine arranged to energize said transformer field exciting winding means including a field exciting winding for said auxiliary dynamo-electric machine for controlling the rate of acceleration of said driving motors, an emergency electrical load absorbing means including an emergency braking resistor, means for inserting and removing said emergency load absorbing means in circuit with said one of said motors between said motor and said dynamoelectric transformer brushes, a main electrical load absorbing means including a main load resistor, means in circuit with said main load absorbing means for connecting said main load absorbing means across said primary brushes, means dependent on the electrical potential across said primary brushes for opening and closing the circuit of said main load absorbing means circuit connecting means, an auxiliary electric generator mechanically driven by said dynamo-electric transformer, an auxiliary electrical load, and means dependent on the electrical potential across said primary brushes for com necting and disconnecting said auxiliary elec trical load to said auxiliary generator.

HAROLD G. MOORE.

FREMONT FELIX. 

